Canal Configuration of Mesiobuccal Roots in Permanent Maxillary First Molars in Iranian Population: A Systematic Review.

OBJECTIVES
It is essential for clinicians to have adequate knowledge about root canal configurations; although its morphology varies largely in different ethnicities and even in different individuals with the same ethnic background. The current study aims to review the root canal configurations of mesiobuccal roots of maxillary first molars in an Iranian population based on different epidemiological studies.


MATERIALS AND METHODS
A comprehensive search was conducted to retrieve articles related to root canal configuration and prevalence of each type of root canal based on Vertucci's classification for the mesiobuccal root of maxillary first molars. An electronic search was conducted in Medline, Scopus and Google Scholar from January 1984 to September 2015. The articles were evaluated and methods, population, number of teeth and percentage of each root canal type evaluated in each study were summarized in the data table. Websites such as http://www.magiran.com/ , http://health.barakatkns.com/journal-internal-list and www.sid.ir were used to search all related studies published in Persian.


RESULTS
Totally, out of nine studies conducted on the Iranian populations in nine provinces of Iran and 798 teeth, the Vertucci's type I was the most common type (35.70%), followed by type II (30.37%), type IV (16.66%), type III (7.93%) and type V (2.61%).


CONCLUSIONS
From this review article, it is concluded that the root canal morphology of mesiobuccal roots of maxillary first molars in the Iranian population predominantly has more than one canal. Therefore, careful evaluation of radiographs and anatomy of the pulp chamber is essential in order to achieve a successful root canal therapy.


INTRODUCTION
Successful nonsurgical endodontic therapy is closely associated with locating all root canals, properly cleaning and shaping them both mechanically and chemically, and perfect obturation using appropriate sealant and root canal filling materials [1][2][3][4][5]. Therefore, it is essential for clinicians to have adequate knowledge about root canal configurations; although its morphology varies largely in different ethnicities and even in different individuals with the same ethnic background [6][7][8]. Root canal configuration is usually complicated and diverse [1,9,10]. Based on the literature, in addition to ethnicity, age [11][12][13][14] and gender [15][16][17] can also influence these diversities. Previous studies classified root canal morphology in various ways [12,18,19]. First, in 1902, GV Black discussed human tooth morphology [20]. In 1969, Weine et al, [19] described a four-type classification method based on the pattern of division of the main root canal. In 1984, the details of human root canals were studied by Vertucci [18]. Vertucci [18] introduced a standardized and categorized method for differentiating the root canal variations into eight descriptive types [18]. This classification has been widely used in many studies [3,6,7,[21][22][23][24][25]. Fourteen new canal morphology types were added to these previous classifications [17]. However, many case reports indicate several variations that emphasize on complete evaluation of each case [26][27][28][29][30]. These variations make it difficult to accurately locate, clean and fill a root canal, and can lead to posttreatment complications and compromise the outcome of root canal therapy [31-33].
Although the most common root canal configuration for permanent maxillary first molars is three roots and four canals [34], several studies have reported uncommon anatomical variations in these teeth [27,35,36]. Due to the wide buccolingual dimension of mesiobuccal root and presence of concavities on its mesial and distal surfaces, two canals are more common in these roots as compared to the distobuccal and palatal roots [1]. These facts have been confirmed by several studies on mesiobuccal roots of maxillary first molars (Table 1).  [55]. Moreover, computed tomography (CT), spiral CT, micro CT and cone beam CT (CBCT) have been used for clinical investigations [4,57,56]. All these methodological and biological factors contribute to variations in the reported prevalence. The current study aims to review the root canal configurations of mesiobuccal roots in maxillary first molars among the Iranian population based on different epidemiological studies.

Literature search and data extraction:
A comprehensive search was conducted to retrieve published and unpublished articles related to root canal configuration and prevalence of each type of root canals based on the Vertucci's classification [18] in mesiobuccal root of maxillary first molars. An electronic search was conducted in Medline, Scopus and Google Scholar from January 1984 to September 2015 without language limitation in publications with available full texts using the following keywords: root canal anatomy, root configuration, root canal morphology and maxillary first molars. Moreover, similar search strategy was also applied for the Cochrane database and manual searches, including journals and reference lists. Two independent reviewers retrieved articles according to the defined keywords. They also performed initial screening on titles and abstracts of the selected articles according to the pre-defined eligibility criteria. Disagreement between reviewers was resolved by discussion and if still remained, a third person was consulted. Eligibility criteria: All in vitro studies evaluating the canal configuration of mesiobuccal roots of permanent maxillary first molars were included in this study. Clinical studies and those assessing other teeth were excluded. Studies only conducted on the Iranian population, which used the Vertucci's classification were included and other populations and methods of classification were excluded. A total of 573 studies were found in the preliminary search. Then, their titles and abstracts were assessed to determine appropriate and related articles. After exclusion of irrelevant studies, 78 articles remained. Then, the full texts of the selected articles were obtained and reviewed. From each study, the methodology, sample size, sampling location and prevalence of different types of root canal configurations were extracted. Among the studies, 16 articles remained with their data and classification based on the Vertucci's classification and only two studies had been conducted on the Iranian population [22,25].
Websites such as www.magiran.com, http://health.barakatkns.com/journal-internal-list and www.sid.ir were used to search all related studies published in Persian. From a total of 31 articles found as such, eight met our inclusion criteria. In addition, to collect unpublished or published regional data related to our study, a request was sent to all dental research centers and dental schools in Iran and nine studies were obtained as such. Finally, Data were collected on: 1) Author and year of publication; 2) Type of study; 3) Method of study; 4) Region of study; 5) Sample size, and 6) Type of root canal morphology.

Included studies:
Among 573 studies, in which anatomy and morphology of maxillary first molars and mesiobuccal canals were evaluated, 78 studies on root canal configurations were selected.
Anatomy and morphology of human extracted teeth were evaluated after access cavity preparation in included studies. Reference lists of included studies were evaluated to identify any potentially relevant article. Ten studies which were conducted on mesiobuccal canal configurations of maxillary first molars in the Iranian population met the inclusion criteria with a total of 649 teeth ( Table 2). All of them were evaluated with clearing technique, direct observation, CBCT and radiography after cavity or section preparation.

Data summary of included studies:
In 2004, Sadeghi and Sadr Lahijani [58] demonstrated that the most frequent type of root configuration among mesiobuccal roots of maxillary first molars was type IV (40%) in Kerman population. In their study, 50 human maxillary first molars were investigated by staining and clearing to determine the type and number of root canals and also the presence of accessory and lateral canals, which had a prevalence of 32% and 8%, respectively. Onehundred and five extracted maxillary first molars were evaluated in another study [59], in which after cavity preparation, the teeth were immersed in 1% fuchsin, incubated and root canal configurations were assessed by radiography and also observation of cross sections. The most common type was type III (39%). Shahi et al, [25] performed demineralization and Indian ink injection and evaluated the specimens by the use of a magnifying-glass at x5 magnification.  [61] indicated the presence of second mesiobuccal canal in 12.5% of teeth, which may be due to small sample size (32 maxillary first molars). In total, as shown in the results of the present study, type I was the most common canal configuration of mesiobuccal root in maxillary first molars in the Iranian population (38.55%), followed by type II (29.54%), type IV (16.41%), type V (12.41%) and type III (6.92%). Finally, these findings indicate that the internal root canal morphology of maxillary first molars, especially the mesiobuccal roots, has never been straight forward.

CONCLUSION
Our study demonstrated that mesiobuccal roots of maxillary first molars in the Iranian population predominantly have more than one canal. Other morphologies have been rarely reported. Therefore, careful evaluation of radiographs and the anatomy of the pulp chamber is essential to achieve a successful root canal therapy. Clinicians should focus on each case individually in addition to their anatomical knowledge.